Apple putting PA Semi talent to work on iPhone chip

Apple's April purchase of PA Semi came as a surprise to most observers. Now we …

When the news broke in April that Apple had purchased low-power chipmaker PA Semi, savvy Apple watchers quickly zeroed in on the reason for the purchase that seemed to make the most sense: Apple could use PA Semi's extremely talented team of experience low-power processor designers to make chips for its iPhone and iPod lines. (The other option, that Apple would somehow use PA Semi's dual-core PowerPC products, was never realistic.) Well, it turns out that this speculation was correct, and Apple will indeed be drawing on PA Semi's formidable design talent in order to fill the iPhone with custom system-on-chip (SoC) parts that will be fabricated by an as yet unnamed manufacturing partner.

A fantasy fulfilled, sort of

An Apple that designed its own processors was a common fantasy back when the company was on the losing end of the PowerPC versus x86 wars. In the lean Motorola years, Apple apologists dreamed of a world in which their favorite computer maker would have an in-house processor design team that would churn out blazingly-fast RISC CPUs for leading-edge Apple workstations, sort of SGI back in its heyday.

Obviously, this dream didn't work out, but the shocking news of the PA Semi did resurrect it, if only briefly. Some speculated that the days of the Apple-Intel partnership were numbered, and that Mac might one day feature the Apple-designed CPU that many fans had once dreamed of. Steve Jobs quickly quashed such speculation, assuring the faithful that his company's partnership with Intel was here to stay.

But it turns out that PA Semi will indeed be designing chips for Apple's most popular line of computing products—not the Mac, but the iPhone and iPod lines.

In a recent interview with John Markoff of TheNew York Times, Jobs said, "PA Semi is going to do system-on-chips for iPhones and iPods."

Though there aren't any more details available than the quote above, it's plausible to infer that the SoCs in question will be ARM-based. Some of the key members of the PA Semi team were formerly part of Intel's XScale group, which designed a line of low-power, ARM-based embedded processors before being sold off as part of a company-wide restructuring.

So Apple basically owns the old Intel XScale team, plus some other talent and IP that the company can put to work immediately. The designs that this team turns out can be fabbed by a foundry partner, potentially on a process that's close to leading-edge, and used exclusively in Apple products. This exclusivity could give Apple an edge in the increasingly crowded ARM media SoC market. Or, alternately, it could be a waste of money. Let's look at both options in turn, starting with the latter.

It fits like a rented suit

I suggest that the PA Semi effort might be a waste, because the ARM ecosystem is very competitive right now, and growing more so by the day. Apple will have a ton of options to choose from next year, if the company wants good, low-power media SoCs that incorporate an ARM core and a GPU core on the same die, or two ARM cores. That competition is healthy, and will drive plenty of innovation in the ARM ecosystem. So it could be to Apple's disadvantage if it goes off and does its own proprietary thing, instead of selecting the best options from a thriving marketplace.

But the peculiar needs of extremely low-power devices, like phones, can work against even the most option-rich market. What I mean is this: An off-the-shelf SoC is kind of like a rented suit that you can't tailor. You just have to find the best fit for your profile, and just deal with the fact that it's too tight in some places and has extra fabric in others.

This rented suit approach can be fine if you start with what's on the market and design around it, but it works less well when you do like Apple and engineer the phone from the outside in. If Apple uses a commodity media SoC, then that SoC might have, say, a ton of USB interface hardware on it that the iPhone just doesn't need. So by going the in-house, custom route, Apple can tailor the device to meet the exact needs of the mobile product, leaving out any functional blocks that aren't necessary.

Now that some foundries are trailing Intel by under a year in process transitions, Apple can have its bespoke SoCs fabbed on a leading-edge process. This way, the company gets the best of both worlds: complete control over the device, and feature sizes that are competitive with anything on the market.

Right now, I'm leaning towards thinking that the custom SoC route is a great move for Apple, based on the advantages I just listed, and if, for any reason, Apple ever decides that they want to move from ARM to x86 for their portable products, they can always just sell the team to Intel so that they can be put to work on x86 designs.

Further reading

CNET's Tom Krazit also has some analysis of this, along with the related CUDA news, which I have much more to say about at a later time.